The incidence of ventricular fibrillation during reperfusion of ischemic myocardium after release of coronary artery occlusion is reduced by 1) restriction of blood flow during reperfusion with a partial occluder or 2) increased collateral flow to the ischemic myocardium induced by chronic stenosis of an adjacent coronary artery. This suggests that the risk of ventricular fibrillation during relief of coronary spasm in patients may be greater in patients without coronary disease than in those with coronary disease.